Year: 2024
Type: article
Abstract: Although flower nectar is the most conspicuous and energetically efficient food source of hummingbirds, it is notably deficient in amino acids and other essential nutrients (Baker and Baker 1975, Hainsworth and Wolf 1976).Therefore, hummingbirds require an additional source of proteins, lipids, and other nutrients.In most or all species, these nutrients are obtained by consuming small arthropods.Yet arthropod-foraging by hummingbirds remains very little studied compared with nectar-foraging (Gass and Montgomerie 1981, Hespenheide and Stiles unpubl.data).The few available time-budget studies of foraging hummingbirds (reviewed by Gass and Montgomerie 1981) indicate that arthropod-hunting constitutes only 2-12% of total foraging time except when nectar is scarce or unavailable.An incubating female Broad-tailed Hummingbird (Selasphorus platycercus) consumed only arthropods for about 10 days when nectar was unavailable (Montgomerie and Redsell 1980).Thus, under some field conditions a hummingbird can satisfy energetic as well as nutritional needs by feeding exclusively on arthropods.The contents of stomachs and crops of collected birds represent an obvious source of dietary information.Because these data are recorded routinely on specimens collected by our institutions, the specimens can provide an indication of the frequency and generality of arthropod-foraging in hummingbirds.Accordingly, we recorded the presence or absence of arthropod remains in the stomachs and crops of !,629 specimens of 140 species of hummingbirds (41% of the approximately 340 species in the family Trochilidae).Presence of arthropods in the digestive tract of a specimen indicates only that the bird had recently fed on arthropods; it tells us nothing about the relative frequency of arthropods vs. nectar in the diet.It is well known that different kinds of foods have different digestibilities, rates of gut passage, and detectabilities; nectar and arthropods exemplify this problem in the extreme.Nectar is virtually 100% assimilable (Hainsworth 1974, Hainsworth and Wolf 1972) and is rarely detected in the stomach because it usually passes directly from esophagus to intestine (the openings of these are closely apposed in hummingbird stomachs).Arthropods are extensively digested in the stomach, following only brief storage in the crop.Soft-bodied arthropods, such as most small spiders, may be digested relatively quickly, except for easily overlooked poison claws.Many chitinous insect parts (e.g.wings, head capsules) are easily detectable for considerably longer periods.In this pa-per we do not record in detail the kinds of arthropods consumed, except insofar as this may affect the frequency of detectable arthropod remains.A detailed study of the arthropod diets and foraging tactics of hummingbirds is in preparation (Hespenheide and Stiles unpubl.data).The specimens reported here were collected (1) from 1980 to 1985 by personnel of the Museum of Zoology, Louisiana State University (LSUMZ) or (2) from 1971 to 1985 by Stiles and his students.Approximately 70% of all specimens were collected in Bolivia or Peru, 25% in Costa Rica, and the remainder in northwestern Ecuador, Venezuela, or Darign, Panama.Twenty recent specimens of 15 species from Ecuador and Peru deposited in the Academy of Natural Sciences, Phildelphia, also were included.Although specimens were obtained from throughout the year, the sample from Peru and Bolivia is mostly from May through August, the "dry" season.Most (>95%) birds from group !above were captured in mist nets, which were checked from dawn to dusk at 3-4-h intervals; the remainder were shot.Birds from group 2 were collected from mist nets checked at least hourly, or were shot, in roughly equal proportions.Stomachs and crops of group !birds were scored on specimen labels as containing "insects" (including other arthropods), as containing unidentifiable material, or as being "empty."Group 2 birds were scored in greater detail, but the data were converted to one of the three categories used for group !birds.Although not usually recorded on the labels, stomachs that contained arthropods were almost always packed with material rather than containing just a trace of parts.Because soft insects and spiders can be digested completely within 3-4 h (Stiles unpubl.data), our sampling procedure for mist-netted birds is conservatively biased against detection of arthropods.Also, many of the stomach contents of group !specimens scored as "unidentifiable" were presumably the remains of soft insects and spiders.Most (1,279 of 1,629, 79%; see Appendix) hummingbird stomachs and crops contained arthropodremains.Individuals of 133 (95%) of the 140 species examined had been feeding on arthropods.Of the 7 species for which arthropods were not recorded, the largest sample size was only 5 individuals.Few significant regional differences were detected between samples of the same species; therefore, data from all areas were pooled in the Appendix.The main exceptions were several species of hermits (Phaethorninae: genera Glaucis through Eutoxeres).In stomachs of these species arthropods occurred with 436
Authors: Remsen, J. V., Jr., Stiles, F. Gary, Scott, Peter E.
Institution: Universidad de Costa Rica
Language: English
Topic: Avian ecology and behavior
Subfield: Ecology
Field: Environmental Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2523894244